Disposable absorbent products have been known for some time, including such products as disposable diapers, sanitary wound dressings, bandages, incontinent pads, and the like. These products incorporate an absorbent batt that is used to absorb and hold or contain body fluids. In years past, in many of these products, especially diapers and sanitary napkins, the absorbent batt comprised what is termed "wadding" or plies of tissue. The wadding was disposed between an impermeable backing sheet and a permeable facing sheet and the plies of tissue were used to absorb and contain the liquid within the product.
The wadding type of batt was replaced, for the most part, by an improved absorbent batt comprised of fluffed wood pulp fibers. This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. This diaper has improved absorbent capacity and somewhat better containment than a diaper using a wadding layer. Also the fluffed wood pulp layer is quite soft, flexible and conformable and hence, produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the efficiency with which the capacity is used in a diaper or sanitary napkin is poor. The reason for this, is that the fluid to be absorbed is generally deposited in a localized area within the absorbent batt and the ability for the fluid to wick along the plane of the batt is poor. The fluid follows the path of least resistance and consequently moves to the closest edge of the batt where it generally is no longer contained and the product leaks. Furthermore, the wood pulp batts lack stability, e.g., when a diaper is being worn, the batt tends to sag and/or break up thereby creating bunching.
U.S. Pat. No. 3,017,304 discloses an absorbent product which incorporates in the batt a densified, paper-like layer. This paper-like layer acts as a wick, i.e., liquid which contacts the layer tends to move rapidly along the plane of the layer. When incorporated in combination with fluffed wood pulp fiber, the resultant product uses the absorbent capacity of the fluffed wood pulp much more efficiently. Diapers which incorporate this paper-like layer combined with fluffed wood pulp are disclosed and described in U.S. Pat. Nos. 3,612,055 and 3,938,522. Even though these products make much greater use of the capacity of the absorbent batt, they still do not totally contain the absorbed liquid.
A number of years ago "superabsorbent materials", i.e., materials which will absorb many times their weight of liquid, were developed. Since the development of such materials, various different approaches have been suggested to incorporate them in absorbent products such as diapers and sanitary napkins to enhance the absorptive performance of these products. Perhaps one of the first proposals to incorporate such a superabsorbent material in a disposable diaper is disclosed in U.S. Pat. No. 3,670,731. This patent discloses an absorbent dressing comprising an absorbent layer sandwiched between a permeable facing sheet and an impermeable backing sheet. The absorbent layer contains water insoluble cross-linked hydrocolloid polymer as the superabsorbent material.
In order for a superabsorbent material to function the liquid being absorbed must be transported to the superabsorbent material. In other words, the superabsorbent material must be placed in a position to be contacted by liquid discharged onto the absorbent body. Furthermore, as the superabsorbent material absorbs the liquid, it must be allowed to swell. If the superabsorbent is prevented from swelling, it will cease absorbing liquid. Hence, if the superabsorbent material is to function in diapers and sanitary napkins wherein the liquid to be absorbed is discharged in a small void area, the structure of the absorbent layer containing superabsorbent materials appears to be critical. Over the years a number of techniques have been disclosed in an attempt to provide structures which make efficient use of the superabsorbent material. Such products are typified by those in U.S. Pat. Nos. 4,103,062, 4,102,340, and 4,235,237. In addition, methods have been proposed for incorporating superabsorbents into suitable layers or suitable configurations which can be placed in an absorbent product, and examples of such proposals are disclosed in U.S. Pat. Nos. 4,186,165, 4,340,057, and 4,364,992.
In U.S. Pat. Nos. 4,500,315, 4,537,590, 4,540,454, 4,573,988, 4,596,567 and 4,605,402 particularly useful absorbent products are disclosed that include superabsorbent materials and utilize a substantial portion of such absorptive capacity of such superabsorbent materials. These products include a nonwoven fibrous web, such as polyester, which has associated with it at least 200 percent by weight, dry basis, of superabsorbent material to the dry basis weight of the web, to form an absorbing layer. In such products, in order to provide a product which will not only absorb liquid but also transport liquid, a wicking layer of wood pulp fibers or other suitable wicking materials are formed in a layer on at least one side of the absorbing layer. The product is then compressed to yield a relatively thin absorbing product with very substantial liquid absorbing capacity. However, the resulting compressed composite product is quite stiff, and hence it is preferred to soften the product to provide enhanced flexibility for utilization in products such as disposable diapers and the like. One method of reducing the stiffness of these products is to subject them to microcorrugating and then to perfembossing to reduce the stiffness in the manner as described in U.S. Pat. No. 4,605,402.
Fluff and wadding absorbent panels that have been used since the early 1970's were considered by those skilled in the art as being semi-rigid, at least when compared to more flexible portions of a diaper, such as a side flap. In U.S. Pat. No. 3,860,003 such known semi-rigid panels are characterized as a panel that has a Taber stiffness value of greater than 7. Efforts to develop suitable absorbent panels having a Taber stiffness value of less than 7 that function in disposable diaper constructions having side flaps have been attempted, but not met with success. Heretofore it was not thought possible to provide an absorbent panel that would provide adequate absorptive capacity, and yet have a Taber stiffness value less than about 7.
The present invention provides a new and improved absorbent structure that is thin and has a Taber stiffness value in the machine direction of less than about 7 and more preferably less than about 6. More specifically, the invention provides a new and improved superabsorbent containing absorbent panel structure for use in a disposable diaper, or the like, that is thin and has a Taber stiffness value less than about 6 and yet, surprisingly, has an absorptive capacity of at least about 300 ml and more preferably at least about 400 ml.